This invention relates to power line protection and more particularly to a novel method and apparatus for interrupting the flow of current in a three-wire, single-phase energy supply circuit in the event an open neutral line condition is created even when loads are not connected to the energized lines.
It is well known in the power distribution art that the neutral line of a three-wire, single-phase energy supply system may become an open circuit due to improper installation or physical damage. If unequal loads are connected between such open neutral line and each of the pair of energized lines, the load having the lower power requirement, and therefore the higher resistance, will have more than one half the total line-to-line voltage appearing across that load and may be damaged by the resulting additional voltage. Similarly, the higher wattage load will have less than half the line-to-line voltage appearing across that load and may be damaged by the resulting severe undervoltage. Additionally, many large home and commercial appliances operate from three-wire single-phase mains and utilize the neutral line as shock-protective means connected to the equipment case. An open neutral line to such installation creates a severe personnel shock hazard.
Open neutral line protection methods and circuits previously known to the art have either been complex or operable only if a load was connected between each energized line and the neutral line.